Autism spectrum disorder and intellectual disability (ASD/ID) are severe neurodevelopmental conditions with early childhood onset. Advances in genetics have illustrated that ASD/ID represent a spectrum of rare disorders and that mutations in hundreds of genes may result in susceptibility to ASD/ID. This heterogeneity represents significant challenges but at the same time unique opportunities for research in the field of ASD/ID. Many of the genes implicated in ASD/ID appear to converge on a few common pathways, suggesting that there may be a common dysfunction at the cellular or systems level. Deeper understanding of the shared pathophysiology of these diseases may serve as gateways for understanding mechanisms of other causes of ASD/ID and for shared treatment possibilities. Here we focus of three well-established genetic syndromes that are associated with high penetrance for ASD/ID: TSC1/2, PTEN and SHANK3 mutations. Specific aims for TSC are: 1) characterize the developmental phenotype of ASD and ID in a large cohort of pediatric patients with TSC; 2) identify biomarkers using advanced MR imaging; 3) establish infrastructure for the collection and storage of human bio-specimens, including genetic material, from TSC patients and their family members with ASD. Specific aims for PTEN are: 1) determine cross-sectional and longitudinal medical, behavioral, and cognitive differences between PTEN ASD and other groups; 2) identify cognitive, neural systems, and molecular biomarkers specific to PTEN ASD; 3) create and maintain a biorepository and linked phenotypic database for PTEN ASD. Specific aims for SHANK3 are: 1) characterize PMS using standardized medical, behavioral, and cognitive measures and to track the natural history of the syndrome using repeated longitudinal assessments; 2) identify biomarkers using advanced MR imaging; S) identify genetic factors that contribute to diverse phenotypes in patients with PMS. As detailed in the resources sections, this Consortium involves experienced physician researchers from premier academic institutions with strong institutional support, impressive mentors for training of future physician researchers, and long-standing connections to patient advocacy organizations with extensive recruitment networks.